1. Field of the Invention
The invention relates to an oscillator circuit comprising a phase control loop including a phase detector which has a first input coupled to an output of an oscillator, a second input coupled to a comparison signal input of the phase control loop and an output circuit coupled to a current-source circuit which is switchable by means of the output circuit for controlling the charge of a capacitor from which a control signal for the oscillator is obtained.
2. Description of Related Art
An oscillator circuit of the type described above is known from U.S. Pat. No. 4,244,043.
Such an oscillator circuit may be used, for example as a clock signal generator for memory circuits in video signal processing circuits if the comparison signal is a line frequency signal and if the output of the oscillator is coupled via a frequency divider to the first input of the phase detector.
To improve the behavior of the phase control loop, for example FIG. 16 of the above cited United States patent proposes to arrange a resistor in series with the capacitor.
If the oscillator circuit is an integrated circuit, it is found to be difficult to choose a suitable value for this resistor.
The spreads in the gain of the phase detector, in the control slope of the oscillator and in the value of the resistor itself are such that in that case, the properties of the control loop are not fixed.